1. Field of the Invention
This invention relates generally to a method and apparatus for reducing heating effects of an exhaust plume on an impinged surface.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Jet engine exhaust plumes can have deleterious heat effects on impinged surfaces—especially where, as with VSTOL type aircraft, exhaust plumes are sometimes aimed directly downward onto ground or deck surfaces. Also, some aircraft have auxiliary power units that, when the aircraft is resting on the ground or a deck surface, may exhaust very hot low speed flow toward the ground or deck surface—even when a main propulsion jet of such an aircraft is not operating. Temperatures reached by the exhaust plumes from aircraft are quite high, typically upwards of 1,000 degrees F. In fact, when such a plume is directed downward, the high temperature will tend to melt tarmac, erode concrete, and heat metal plates to unacceptably high temperatures. VSTOL aircraft operations are often restricted, as a result, and take-off or landings often must be performed with some forward movement to reduce damage to runway and ramp surfaces.
The deleterious heat effects of an exhaust plume may be reduced by mixing ambient air with the exhaust plume. This has been done by pulsing air flow into the plume through injection nozzles in a way that causes the exhaust plume to “flap” back and forth, mixing with ambient air. Exhaust plumes have also been caused to mix with ambient air by pulsing a circumferentially-spaced array of radially-inwardly-directed air injection nozzles out of phase with one another. Air injection nozzles have also been positioned at converging angles towards the longitudinal axis of an exhaust plume to break up a shear boundary of the plume, causing the exhaust plume to engulf ambient air and introducing large scale vortices into a core of the exhaust plume. Both fan bypass air and compressor bleed air have been used as fluid sources to supply fluid injection nozzles in such systems.
To shorten the downstream distance at which personnel can work behind a running jet engine, zero-net-mass-flux (ZNMF) actuators have been used to inject fluid with zero net mass flow into a horizontal jet engine exhaust plume and then alternately turned on and off out-of-phase with one another to move the plume upward and downward in a “whipping” motion.